Circuit and method for driving light source

Abstract

A driving circuit for a light source is provided. The circuit is suitable for a light source with a plurality of light emitting diodes (LED). The circuit includes a first pulse width modulation (PWM) unit and a power conversion unit. The first PWM unit generates a first PWM signal. The power conversion unit generates a driving voltage signal for controlling the light source to perform forward bias operation or reversed bias operation according to the duty cycle of the first PWM signal.

1 . A driving circuit for a light source comprising at least one light emitting diode (LED), the driving circuit comprising:
 a first pulse width modulation (PWM) unit, for generating a first PWM signal whose duty cycle is variable; and   a power conversion unit, for generating a driving voltage signal for controlling the light source to perform a forward bias operation or a reversed bias operation according to the first PWM signal,   wherein the light source is controlled to perform the reversed bias operation for heat dissipation.   
     
     
         2 . The driving circuit as claimed in  claim 1 , wherein the duty cycle of the first PWM signal is a first duty cycle when the light source performs forward bias operation, and the duty cycle of the first PWM signal is a second duty cycle when the light source performs reversed bias operation. 
     
     
         3 . The driving circuit as claimed in  claim 1 , wherein the cathode of the LED is grounded through a second power supply, and the second power supply provides a second voltage signal. 
     
     
         4 . The driving circuit as claimed in  claim 3 , further comprising a second PWM unit for generating a second PWM signal to determine whether or not to send out the driving voltage signal for adjusting a brightness of the light source, and when the driving voltage signal is not sent out, the second voltage signal controlling the light source performs the reversed bias operation. 
     
     
         5 . The driving circuit as claimed in  claim 1 , wherein the anode of the LED is grounded through a third power supply, and the third power supply provides a third voltage signal. 
     
     
         6 . The driving circuit as claimed in  claim 5 , further comprising a second PWM unit for generating a second PWM signal to determine whether or not to send out the driving voltage signal for adjusting a brightness of the light source, and when the driving voltage signal is not sent out, the third voltage signal controlling the light source performs the reversed bias operation. 
     
     
         7 . The driving circuit as claimed in  claim 1 , further comprising:
 a switch, disposed between the power conversion unit and the light source; and   a second PWM unit, for generating a second PWM signal to determine an on/off status of the switch so as to adjust a brightness of the light source.   
     
     
         8 . The driving circuit as claimed in  claim 1 , further comprising a thermo sensor for detecting the operation temperature of the light source, wherein when the operation temperature of the light source exceeds a predetermined value, the thermo sensor generates a detection signal, the first PWM unit adjusts the duty cycle of the first PWM signal according to the detection signal to allow the driving voltage signal to change along time to make the light source perform a reversed bias operation and a forward bias operation alternatively along time. 
     
     
         9 . The driving circuit as claimed in  claim 1 , wherein the power conversion unit comprises:
 a switch component, receiving the first PWM signal;   a first inductor, having one terminal receiving a DC bias and another terminal coupled to the switch component;   a second inductor;   a first capacitor, having one terminal coupled to the switch component and another terminal grounded through the second inductor;   a diode, having its anode coupled to a terminal of the first capacitor and grounded through the second inductor; and   a second capacitor, having one terminal coupled to the cathode of the diode and another terminal grounded.   
     
     
         10 . The driving circuit as claimed in  claim 9 , wherein the switch component is a transistor, the first source/drain of the switch component is grounded, and the gate of the switch component receives the first PWM signal. 
     
     
         11 . The driving circuit as claimed in  claim 1 , wherein the power conversion unit is a buck-boost circuit. 
     
     
         12 . The driving circuit as claimed in  claim 11 , wherein the light source performs a forward bias operation when the duty cycle of the PWM signal generated by the PWM unit is more than 50%. 
     
     
         13 . The driving circuit as claimed in  claim 11 , wherein the light source performs a reversed bias operation when the duty cycle of the PWM signal generated by the PWM unit is less than 50%. 
     
     
         14 . A driving method for a light source, wherein the light source comprises at least one LED, and the driving method comprises:
 controlling the LED to perform a forward bias operation during a first time period, so that the light source operating normally; and   controlling the LED to perform a reversed bias operation during a second time period for heat dissipation.   
     
     
         15 . The driving method as claimed in  claim 14 , further comprising:
 generating a PWM signal whose duty cycle is variable;   controlling the PWM signal into a first predetermined duty cycle during the first time period to generate a driving voltage signal at a first level for driving the light source, and   controlling the duty cycle of the PWM signal into a second predetermined duty cycle during the second time period to generate the driving voltage signal at a second level for driving the light source, wherein the second level is lower than the first level.   
     
     
         16 . The driving method as claimed in  claim 15 , further comprising adjusting the duty cycle of the PWM signal when the operation temperature of the light source exceeds a predetermined value. 
     
     
         17 . The driving method as claimed in  claim 14 , wherein the first time period is longer than or equal to the second time period. 
     
     
         18 . The driving method as claimed in  claim 14 , further comprising:
 providing a PWM signal whose duty cycle is variable;   controlling the duty cycle of the PWM signal to be more than 50% during the first time period to generate a driving voltage signal at a first level for driving the light source; and   controlling the duty cycle of the PWM signal to be less than 50% during the second time period to generate the driving voltage signal at a second level for driving the light source, wherein the second level is lower than the first level.   
     
     
         19 . A LED driving circuit, comprising:
 a power conversion unit, coupled to a input voltage, for converting the input voltage into an output voltage for driving a LED module according to a control signal; and   a control unit, for generating the control signal for controlling the LED module to perform forward bias operation and reversed bias operation alternately   wherein the LED module is controlled to perform the reversed bias operation for heat dissipation.   
     
     
         20 . The LED driving circuit as claimed in  claim 19 , wherein the power conversion unit comprises a DC/DC converter and a bias module, the DC/DC converter is coupled to a first terminal of the LED module, and the bias module is coupled to a second terminal of the LED module. 
     
     
         21 . The LED driving circuit as claimed in  claim 19 , wherein the power conversion unit comprises two DC/DC converters, one of the two DC/DC converters is coupled to a first terminal of the LED module, and another one of the two DC/DC converters is coupled to a second terminal of the LED module.